1. Technical Field
This disclosure generally relates to flash memory, and more specifically relates to dynamically adjusting read voltage in a NAND flash memory.
2. Background Art
Flash memory is a particular type of non-volatile storage, meaning flash memory does not required power to retain data. NAND flash memory is a particular type of flash memory that defines blocks of data that can be written without writing the entire memory. While NOR flash memory typically provides the capability of writing much smaller blocks, even down to the byte level, NAND flash memory provides much greater density and therefore less cost per bit when compared to NOR flash memory. NAND flash memory has become very popular in applications such as MP3 audio players, digital cameras, and universal serial bus (USB) drives.
There are different types of NAND flash memory according to the storage capability of each flash memory cell. Single-Level per Cell (SLC) can store two distinct states per cell. Multi-Level per Cell (MLC) can store four distinct states per cell. Three-Level per Cell (TLC) can store eight distinct states per cell. The states of the cell are a function of voltage stored on the floating gates of the cell. Thus, a MLC NAND flash memory can store four distinct voltage levels on a cell that are each interpreted as values of two bits in the memory.